All you need to do is to make a pit with a waypoint tagged "FUCKOFFANDDIE". That will be the place the player will teleport to when he killed 3 NPC's. He will receive a warning after every kill, and DM's will receive a message who killed which NPC.
In my module, the Player will be teleported into a pit with a big nasty thing in the commoner faction; it will kill the basterd unless he got there without killing things. Enjoy.

[Edit] It will also record the event in the logfile.

- As you gaze unknowingly into the seemingly infinite depths of the optics of this altogether passionate embodiment of insatiability, you experience a gradual realisation that the heavily-embellished vocabulary scattered lavishly throughout the sentence you are currently reading is indisputably nothing greater than a generous ration of masculine bovine faeces.